# US 9,438,371 B2 · Linear dispersion polarization-time codes and equalization in polarization multiplexed coherent optical system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,438,371 B2 - Document ID: US9438371B2 - Status: Granted - Kind: B2 - Application number: 14/959,918 - Filed: 2015-12-04 - Published: 2016-03-24 - Granted: 2016-09-06 - Earliest claimed: 2012-04-12 - Assignees: Futurewei Technologies, Inc. - Applicants: Futurewei Technologies, Inc. - Inventors: Mahdi Zamani; Chuandong Li; Zhuhong Zhang - Web page: https://patentgrep.com/patent/US9438371B2 ## CPC - H04J 14/06: Polarisation multiplex systems - H04B 10/532: Polarisation modulation - H04B 10/5055: {using a pre-coder} - H04L 27/2697: {in combination with other modulation techniques} - H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S) - H04B: TRANSMISSION - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract A method of optical communication comprising encoding four modulated symbols to generate four encoded symbols in two orthogonal polarizations and transmitting the four encoded symbols in two successive time slots. An optical communication apparatus comprising a processor configured to receive two sequences of digital symbols in a plurality of time slots, wherein the two sequences correspond to two components of two orthogonal polarizations, wherein one digital symbol per polarization is received in each of the plurality of time slots, divide each of the two sequences into a plurality of groups using a modulo operation of time, wherein each group comprises two digital symbols received in two consecutive time slots, and adaptively equalize the four digital symbols of the two consecutive time slots using a 4×4 matrix to generate four modulated symbols, wherein the 4×4 matrix comprises 16 tap-vectors. ## Claims ### Claim 1 An optical communication apparatus comprising: a receiver configured to receive two sequences of digital signals in a plurality of time slots, wherein the two sequences correspond to two components of two orthogonal polarizations, wherein one digital signal per polarization is received in each of the plurality of time slots; a digital signal processor comprising: a pair of frequency-domain equalizers configured to filter the two sequences of digital signals in the frequency domain to generate two frequency-domain equalized sequences; and a multiple-input and multi-output (MIMO) finite impulse response (FIR) equalizer configured to: divide each of the two frequency-domain equalized sequences into a plurality of groups using a modulo operation of time, wherein each group comprises two digital signals received in two consecutive time slots; and adaptively equalize the four digital signals of the two consecutive time slots using a 4×4 matrix to generate four modulated symbols, wherein the 4×4 matrix comprises 16 tap-vectors. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein a group of a first sequence, denoted as rx (t), comprises two digital signals, denoted as rx1 and rx2, wherein t denotes a time, wherein another group of a second input, denoted as ry(t), comprises two signals, denoted as ry1 and ry2, wherein the two orthogonal polarizations are denoted as X and Y, and wherein the modulo operation is: rx1={rx(t)|(t mod2K)ε{0, . . . ,K−1}} rx2={rx(t)|(t mod2K)ε{K, . . . ,2K−1}} ry1={ry(t)|(t mod2K)ε{0, . . . ,K−1}} ry2={ry(t)|(t mod2K)ε{K, . . . ,2K−1}} where K is an integer greater than one. ### Claim 3 (depends on 2) The apparatus of claim 2, wherein K=2. ### Claim 4 (depends on 3) The apparatus of claim 3, wherein each of the tap-vectors is updated based on an error signal computed by comparing an equalized signal and a decision signal. ### Claim 5 (depends on 4) The apparatus of claim 4, wherein the MIMO FIR equalizer is a 4×4 MIMO FIR equalizer, wherein adaptively equalizing the four digital signals is implemented by the 4×4 MIMO FIR equalizer, and wherein the decision signal is generated within the 4×4 MIMO FIR equalizer. ### Claim 6 (depends on 1) The apparatus of claim 1, wherein each of the tap-vectors comprises a plurality of taps. ### Claim 7 (depends on 1) The apparatus of claim 1, wherein the digital signal processor further comprises a 2×2 MIMO FIR equalizer, wherein two outputs of the 2×2 MIMO FIR equalizer in a first time slot and two additional outputs in a second time slot are the inputs of the MIMO FIR equalizer, and wherein each of the tap-vectors comprises one tap. ### Claim 8 A method comprising: receiving, by a receiver, two sequences of digital signals in a plurality of time slots, wherein the two sequences correspond to two components of two orthogonal polarizations, and wherein one digital signal per polarization is received in each of the plurality of time slots; filtering, by a pair of frequency-domain equalizers, each of the two sequences in the frequency domain to generate two frequency-domain equalized sequences: dividing, by a multiple-input and multiple-output (MIMO) finite impulse response (FIR) equalizer of a digital signal processor, each of the two frequency-domain equalized sequences into a plurality of groups using a modulo operation of time, wherein each group comprises two digital signals received in two consecutive time slots; and adaptively equalizing, by the MIMO FIR equalizer, the four digital signals of the two consecutive time slots using a 4×4 matrix to generate four modulated symbols, wherein the 4×4 matrix comprises 16 tap-vectors. ### Claim 9 (depends on 8) The method of claim 8, wherein a group of a first sequence, denoted as rx(t), comprises two digital signals, denoted as rxl and rx2, wherein t denotes a time, wherein another group of a second input, denoted as ry(t), comprises two signals, denoted as ry1 and ry2, wherein the two orthogonal polarizations are denoted as X and Y, and wherein the modulo operation is: rx1={rx(t)|(t mod2K)ε{0, . . . ,K−1}} rx2={rx(t)|(t mod2K)ε{K, . . . ,2K−1}} ry1={ry(t)|(t mod2K)ε{0, . . . ,K−1}} ry2={ry(t)|(t mod2K)ε{K, . . . ,2K−1}} where K is an integer greater than one. ### Claim 10 (depends on 9) The method of claim 9, wherein K=2. ### Claim 11 (depends on 10) The method of claim 10, wherein each of the tap-vectors is updated based on an error signal computed by comparing an equalized signal and a decision signal. ### Claim 12 (depends on 11) The method of claim 11, wherein the MIMO FIR equalizer is a 4×4 MIMO FIR equalizer, and wherein the decision signal is generated within the 4×4 MIMO FIR equalizer. ### Claim 13 (depends on 8) The method of claim 8, wherein each of the tap-vectors comprises a plurality of taps. ### Claim 14 (depends on 8) The method of claim 8, wherein the two consecutive time slots comprises a first time slot and a second time slot, the method further comprising: using the 4×4 matrix prior to adaptively equalizing the four digital signals; equalizing two of the four digital signals received in the first time slot using a 2×2 matrix to generate two outputs; and equalizing the other two of the four digital signals received in the second time slot using the 2×2 matrix to generate two additional outputs, wherein the two outputs and the two additional outputs are inputs of the 4×4 matrix, and wherein each of the tap-vectors comprises one tap.